The correct option is D.
The major component of rust is Fe2O3. To know the number of atom in one molecule of rust, one have to look at the chemical formula of rust and determine the different atoms that are present and their numbers. Looking at the chemical formula above, one will notice that, two atoms of iron is present and three atoms of oxygen. The number of atoms present are written in front of the chemical symbol of each element. two atoms of iron added to three atoms of oxygen will give 5 atoms. Thus, five atoms are present in one molecule of rust.